Acetic acid bacteria are microorganisms widely utilized for producing vinegar. Particularly, acetic acid bacteria belonging to the genus Acetobacter or the genus Gluconacetobacter are utilized in industrial acetic acid fermentation.
In acetic acid fermentation, ethanol in a medium is oxidized and converted to acetic acid by acetic acid bacteria. As a result, acetic acid accumulates in the medium. Acetic acid is also inhibitory on acetic acid bacteria, and the growth ability and the fermentation ability of acetic acid bacteria gradually decrease as the amount of accumulated acetic acid increases and the concentration of acetic acid in the medium becomes higher.
For example, it has been observed that the period from the initiation of fermentation to the time when acetic acid bacteria actually start growing and the accumulation of acetic acid can be confirmed, i.e., the period referred to as growth induction period, tends to be longer as the concentration of acetic acid becomes higher. It has been also confirmed that the growth rate and the growth amount of acetic acid bacteria decrease as the concentration of acetic acid becomes higher.
In order to improve by breeding the above-mentioned growth ability of acetic acid bacteria in the presence of acetic acid, an effort has been made for obtaining a gene that encodes a protein having a function of promoting acetic acid bacterial growth in the presence of acetic acid and enhancing the acetic acid bacteria's function of promoting growth, thereby developing acetic acid bacteria with an improved fermentation ability in a high concentration of acetic acid. For example, the ompA gene of acetic acid bacteria, which is highly homologous to the ompA gene of Escherichia coli and the like, was cloned and the gene was confirmed to have a function of promoting acetic acid bacterial growth in the presence of acetic acid (for example, see patent document 1), but the effect was less than sufficient.
Further, based on the assumption that there exists a protein involved in the adaptative mechanism to a high concentration of acetic acid, in a group of proteins expressed in acetic acid bacteria being cultured in a high concentration of acetic acid, it has been reported that there are some proteins in the above protein group that are highly homologous to protease I, pectate lyase II precursor, ubiquinone oxidoreductase, chaperon GroEL and the like in terms of N-terminal-side amino acid sequences (for example, see non-patent document 1). It has, however, not been confirmed whether these proteins have a function of promoting acetic acid bacterial growth in the presence of acetic acid.
For the above reasons, it has been awaited to obtain a gene that encodes a protein having a function of promoting growth in the presence of acetic acid and to enhance the acetic acid bacteria's function of promoting growth in the presence of acetic acid by using the gene, thereby to develop acetic acid bacteria with an improved fermentation ability in a high concentration of acetic acid.    Patent Document 1: International Publication No. WO2005/001095    Non-Patent Document 1: Appl. Environ. Microbiol. Vol. 67, pp. 5474-5481, 2001